The fast development of telecommunication services, such as Cellular phones, WiFi, WiMAX, RFID, Digital TV etc., faces different standards, spectrum allocations, and regulations. The portable products for these services move toward highly integrated forms as the technologies progress. To select a desirable signal or service on these products, we have been observing an increasing need exists for switchable and tunable filters for both broadband and multiband systems that are small in size, inexpensive, and easy to manufacture.
Highly integrated portable telecommunication products demand system miniaturization. The design of filters evolves with the miniaturization efforts of System On Package (SOP) and System On Circuit (SOC) technologies accordingly. From the SOP perspective, new generation of filters are assembled with other active and passive RF components, such as integrated circuits and antennas in Low Temperature Co-fired Ceramics (LTCC) packages. From the SOC perspective, active filters make steady progress as the high Q value on-chip inductors improve performance (Kuhn, et al “Dynamic Range Performance of On-Chip RF Bandpass Filter”, IEEE Trans. On Circuits and Systems, Vol. 50, No. 10, October 2003, pp. 685-694). Recently, one of the efforts proposed Photonic Band Gap (PBG) or Electromagnetic Band Gap (EBG) structures on the substrates for the design of bandpass or bandstop filters or for the suppression of high-order harmonics (Y. Qian, V. Radisic, and T. Itoh, “Simulation and experiment of photonic band-gap structures for microstrip circuits”, Asia-Pacific Microwave Conf., Hong Kong, December 1997, pp. 585-588). Other efforts adopted Defected Ground Structure (DSG) to create resonators on the ground plane. This approach resulted in that part of energy with frequencies at DSG resonators' frequencies is coupled to the ground plane and dissipated and constructed bandstop filters.
However, miniaturization does not directly meet the need for switchable and tunable filters for both broadband and multiband applications. Hereby, this invention follows the miniaturization trend and develops switchable and tunable filters based on some of prior arts:    (1) Finite-sized conductor-backed coplanar waveguides    (2) Vias or Via holes including connecting posts    (3) Switches (such as PIN diodes, FET transistors, Thin Film Transistors, MEMS etc.)
Coplanar waveguides was initially proposed by C. P. Wen in 1969 and has been under intensively investigation since this structure can be used for signal transmission and feeding, such as in Microwave Monolithic Integrated Circuits (MMICs) and antennas. For example, the inventor of this invention proposed of using coplanar waveguide for feeding high frequency patch antenna (D. Ni, et al, “Millimeter-Wave Generation and Characterization of a GaAs FET by Optical Mixing”, IEEE Trans. On Microwave Theory and Techniques, Vol. 38, No. 5, May, 1990, pp. 608-614). Since the IC chips are generally attached onto finite-sized packages constructed by metallic and dielectric materials, finite-sized conductor-backed coplanar waveguides have also been studied extensively as shown in the following publications:
M. Riaziat, I. Feng, R. Majidi-Ahy, and B. Auld, “Single-Mode Operation of Coplanar Waveguides”, Electronic Letters, Nov. 19, 1987, Vol. 23, No. 24, pp. 1281-1283;
C-C. Tien, C-K. C. Tzuang, S. T. Peng, and C-C. Chang, “Transmission Characteristics of Finite-Width Conductor-Backed Coplanar Waveguide”, IEEE Trans. On Microwave Theory and Techniques, Vol. 41, No. 9, September 1993, pp. 1616-1624.
Recently, SOP efforts have integrated several active and passive components into millimeter-sized multi-layer LTCC packages, therein coplanar waveguides and the related waveguides once again under intensive modeling and simulation efforts.
Via holes have been playing a crucial roles in MMIC technology. Recently, via holes are also extensively used in multi-layer LTCC packages for connecting signal paths and ground planes across multi-layers. There are studies and measurements on the parasitic parameters, such as inductance and capacitance, as well as interference phenomena. The following publications describe some of these efforts:
K. L. Finch and N. G. Alexopoulos, “Shunt Posts in Microstrip Transmission Lines”, IEEE Trans. On Microwave Theory and Techniques, Vol. 38, No. 11, November. 1990, pp. 1585-1594;
M. E. Goldfarb and R. A. Pucel, “Modeling Via Hole Grounds in Microstrip”, IEEE Microwave and Guided Wave Letters, Vol. 1, No. 6, June 1991, pp. 135-137;
E. Laermans, J. D. Geest, D. Zutter, F. Olyslager, S. Sercu, and D. Morlion, “Modeling Differential Via Holes”, IEEE Trans. On Advanced Packaging, Vol. 24, No. 3, August 2001;
In the studies listed above, Finch and Alexopoulos used via holes in conjunction with microstrip lines to construct bandpass filter at specific frequencies. Along with the development of multi-layer packages, such as LTCC, via holes are used in various areas:    (1) Isolation of signal waveguides from interference;    (2) Formation of walls of resonating cavities;    (3) Formation of connections for grounding;    (4) Use of via holes' parameters, such as length and radius, to adjust inductance and capacitance for the purpose of impedance matching.
The following publications and U.S. patents illustrate these usages of via holes: J. A. Ruiz-Cruz, Y. Zhang, K. A. Zaki, A. J. Piloto, and J. Tallo, “Ultra-Wideband LTCC Ridge Waveguide Filters”, and U.S. Patent Documents: U.S. Pat. Nos. 5,689,216, 6,137,383, 7,053,729 B2, 7,113,060 B2, 7,142,074 B2, 7,170,373 B2.
Switchable and tunable filters take advantage of switching devices (such as PIN diodes, FET transistors, Thin film transistors, MEMS etc.) for connecting modules with different resonating frequencies. In the prior arts, designs of switchable and tunable coplanar filters used PIN diodes and MEMS for selecting or connecting several configurations of cavities or waveguide. Due to the fixed sizes and patterns of these configurations, the switchable types and tunable frequency range are limited. Others used magnetic of ferromagnetic materials, such as Barium Strontium Titanate Oxide (BSTO), for changing impedance and subsequently for tuning the frequencies. However, there are also limitations in frequency response due to the material characterization and manufacture cost. The following publications disclosed these prior arts: US Patent documents: U.S. Pat. Nos. 5,142,255, 5,693,429, 6,606,017, and 7,148,770.